Rapid determination of fungal colonization and arbuscule formation in roots of Medicago truncatula using real-time (RT) PCR.

The quantifications of root colonization and symbiotic activity in the arbuscular mycorrhizal (AM) association of Medicago truncatula and Glomus intraradices were performed by quantitative polymerase chain reaction (real-time PCR). A strong correlation between fungal colonization of the root system and the amounts of fungal rDNA and rRNA were shown. In contrast, the transcript levels of the AM-specific phosphate transporter 4 from M. truncatula (MtPT4) correlate with arbuscule formation rather than with fungal colonization. These results suggest (i) that real-time PCR assay is a rapid, useful, and accurate method for the determination of arbuscular mycorrhizal features, (ii) that the amount of fungal rDNA or rRNA is a good parameter to estimate fungal colonization, and (iii) that it is necessary to evaluate the amount of other transcripts-like the MtPT4 transcript-to obtain additional information about the symbiotic state of the colonized root system.